How websites will signal when they're censored

A new error code, known as 451, could signal that the Web page you're after has been censored.

Governments will not always be able to disguise which content they restrict across the Web thanks to a new error code that will warn you of censorship.

The Internet serves up a range of status codes, numbered from the 100s to the 500s, to let you know when something goes wrong, such as server downtime, to keep you from getting to a given Web page. You're likely familiar with the common 404 error message that tells you a page cannot be found.

It isn't always easy, however, to work out whether a Web page is down because of technical hiccups or governmental meddling. That's where the new 451 code comes in.

On Friday, the group responsible for Internet standards, the Internet Engineering Steering Group, approved a new HTTP code to differentiate between Web pages that cannot be shown for technical reasons and others that are unavailable for non-technical reasons, such as censorship.

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Error 451: The new code for a censored website

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The Internet has long been a target of censors. Governments in the European bloc force Internet service providers to restrict access to websites linking to pirated content, China has a "Great Firewall" that heavily restricts the Web, and countries including Russia and South Korea are known for cracking down on access.

Mark Nottingham, chair of the group of developers who oversee the Web's core protocol known as HTTP, explained in a blog post while the existing 403 error status code says "Forbidden," it does not specify whether there are legal reasons for restricting content.

However, status code 451 -- a hat tip to "Fahrenheit 451," the classic Ray Bradbury tale about a futuristic society fixated on book-burning -- can now be used to distinguish pages unavailable due to censorship.

"As censorship became more visible and prevalent on the Web, we started to hear from sites that they'd like to be able to make this distinction," Nottingham said.

In addition, some organizations said they would like to be able to search the Web for pages containing a censorship-based error code in order to catalog examples of censorship.

Nottingham predicts that the 451 code will likely be used more on Web servers than by network-based intermediaries, as websites including Twitter, Facebook, Google and Github are forced to censor content in certain countries and jurisdictions.

There are also discussions under way concerning how 451 could be used to prompt users to access restricted content in other ways.

"In some jurisdictions," Nottingham wrote, "I suspect that censorious governments will disallow the use of 451, to hide what they're doing. We can't stop that (of course), but if your government does that, it sends a strong message to you as a citizen about what their intent is. That's worth knowing about, I think."